Self-pinned CPP sensor using Fe/Cr/Fe structure

ABSTRACT

A magnetic head having a free layer, an antiparallel (AP) pinned layer structure spaced apart from the free layer, and a high coercivity structure positioned towards the AP pinned layer structure on an opposite side thereof relative to the free layer. The high coercivity structure pins a magnetic orientation of the AP pinned layer structure. The AP pinned layer structure includes at least two Fe-containing pinned layers having magnetic moments that are self-pinned antiparallel to each other, the pinned layers being separated by an AP coupling layer of Cr.

RELATED APPLICATION

This application is related to a U.S. patent application filedconcurrently herewith entitled “High Hc Reference Layer Structure forSelf-Pinned GMR Heads” by the same inventor and assigned to a commonassignee, the Patent Application being herein incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to magnetic heads, and more particularly,this invention relates to sensors having Fe/Cr/Fe structures.

BACKGROUND OF THE INVENTION

The heart of a computer is a magnetic disk drive which includes arotating magnetic disk, a slider that has read and write heads (alsocalled writers and sensors), a suspension arm above the rotating diskand an actuator arm that swings the suspension arm to place the read andwrite heads over selected circular tracks on the rotating disk. Thesuspension arm biases the slider into contact with the surface of thedisk when the disk is not rotating but, when the disk rotates, air isswirled by the rotating disk adjacent an air bearing surface (ABS) ofthe slider causing the slider to ride on an air bearing a slightdistance from the surface of the rotating disk. When the slider rides onthe air bearing the write and read heads are employed for writingmagnetic impressions to and reading magnetic signal fields from therotating disk. The read and write heads are connected to processingcircuitry that operates according to a computer program to implement thewriting and reading functions.

In high capacity disk drives, magnetoresistive (MR) read sensors,commonly referred to as MR heads, are the prevailing read sensorsbecause of their capability to read data from a surface of a disk atgreater track and linear densities than thin film inductive heads. An MRsensor detects a magnetic field through the change in the resistance ofits MR sensing layer (also referred to as an “MR element”) as a functionof the strength and direction of the magnetic flux being sensed by theMR layer.

The conventional MR sensor operates on the basis of the anisotropicmagnetoresistive (AMR) effect in which an MR element resistance variesas the square of the cosine of the angle between the magnetization inthe MR element and the direction of sense current flow through the MRelement. Recorded data can be read from a magnetic medium because theexternal magnetic field from the recorded magnetic medium (the signalfield) causes a change in the direction of magnetization of the MRelement, which in turn causes a change in resistance of the MR elementand a corresponding change in the sensed current or voltage.

Another type of MR sensor is the giant magnetoresistance (GMR) sensormanifesting the GMR effect. In GMR sensors, the resistance of the GMRsensor varies as a function of the spin-dependent transmission of theconduction electrons between ferromagnetic layers separated by anon-magnetic layer (spacer) and the accompanying spin-dependentscattering which takes place at the interface of the ferromagnetic andnon-magnetic layers and within the ferromagnetic layers.

GMR sensors using only two layers of ferromagnetic material (e.g.,Ni—Fe) separated by a layer of non-magnetic material (e.g., copper) aregenerally referred to as spin valve (SV) sensors. In an SV sensor, oneof the ferromagnetic layers, referred to as the pinned layer (referencelayer), has its magnetization typically pinned by exchange coupling withan antiferromagnetic (e.g., NiO or Fe—Mn) layer. The pinning fieldgenerated by the antiferromagnetic layer should be greater thandemagnetizing fields (about 200 Oe) at the operating temperature of theSV sensor (about 120° C.) to ensure that the magnetization direction ofthe pinned layer remains fixed during the application of external fields(e.g., fields from bits recorded on the disk). The magnetization of theother ferromagnetic layer, referred to as the free layer, however, isnot fixed and is free to rotate in response to the field from therecorded magnetic medium (the signal field). U.S. Pat. No. 5,206,590granted to Dieny et al., incorporated herein by reference, discloses aSV sensor operating on the basis of the GMR effect.

An exemplary high performance read head employs a spin valve sensor forsensing the magnetic signal fields from the rotating magnetic disk. FIG.1A shows a prior art SV sensor 100 comprising a free layer (freeferromagnetic layer) 110 separated from a pinned layer (pinnedferromagnetic layer) 120 by a non-magnetic, electrically-conductingspacer layer 115. The magnetization of the pinned layer 120 is fixed byan antiferromagnetic (AFM) layer 130.

FIG. 1B shows another prior art SV sensor 150 with a flux keeperedconfiguration. The SV sensor 150 is substantially identical to the SVsensor 100 shown in FIG. 1A except for the addition of a keeper layer152 formed of ferromagnetic material separated from the free layer 110by a non-magnetic spacer layer 154. The keeper layer 152 provides a fluxclosure path for the magnetic field from the pinned layer 120 resultingin reduced magnetostatic interaction of the pinned layer 120 with thefree layer 110. U.S. Pat. No. 5,508,867 granted to Cain et al. disclosesa SV sensor having a flux keepered configuration.

U.S. patent application Pub. No. 2003/0161077 A1 to Kawawake et al.discloses a structure that uses a Fe/Cr/Fe type spin valve structure andan AFM layer as a magnetization rotation suppression layer. As disclosedtherein, the Fe/Cr/Fe type spin valve provides a large change inresistance, which in turn translates into greater signal.

Another type of SV sensor is an antiparallel (AP)-pinned SV sensor. InAP-Pinned SV sensors, the pinned layer is a laminated structure of twoferromagnetic layers separated by a non-magnetic coupling layer suchthat the magnetizations of the two ferromagnetic layers are stronglycoupled together antiferromagnetically in an antiparallel orientation.The AP-Pinned SV sensor provides improved exchange coupling of theantiferromagnetic (AFM) layer to the laminated pinned layer structurethan is achieved with the pinned layer structure of the SV sensor ofFIG. 1A. This improved exchange coupling increases the stability of theAP-Pinned SV sensor at high temperatures which allows the use ofcorrosion resistant antiferromagnetic materials such as NiO for the AFMlayer.

Referring to FIG. 2, an AP-Pinned SV sensor 200 typically comprises afree layer 210 separated from a laminated AP-pinned layer structure 220by a nonmagnetic, electrically-conducting spacer layer 215. Themagnetization of the laminated AP-pinned layer structure 220 is fixed byan AFM layer 230. The laminated AP-pinned layer structure 220 comprisesa first ferromagnetic layer 226 and a second ferromagnetic layer 222separated by an antiparallel coupling layer (APC) 224 of nonmagneticmaterial. The two ferromagnetic layers 226, 222 (FM₁ and FM₂) in thelaminated AP-pinned layer structure 220 have their magnetizationdirections oriented antiparallel, as indicated by the arrows 227, 223(arrows pointing out of and into the plane of the paper respectively).

As mentioned above, AP-Pinned SV sensors typically use an AFM layer inorder to pin the magnetization so that the pinned layers do not movearound when the head is reading data from the disk, upon application ofexternal magnetic fields, etc. The AFM layers are typically very thick,on the order of 150–200 Å. Due to the large overall thickness, suchsensors are typically not practical for use in applications where a thinhead is desirable.

What is needed is a self-pinned AP-Pinned SV sensor having the signalbenefits provided by Fe/Cr/Fe structures while having a smaller overallthickness.

SUMMARY OF THE INVENTION

The present invention provides the advantages described above byproviding a magnetic head having a free layer, an antiparallel (AP)pinned layer structure spaced apart from the free layer, and a highcoercivity structure positioned towards the AP pinned layer structure onan opposite side thereof relative to the free layer. The high coercivitystructure pins a magnetic orientation of the AP pinned layer structure.

The AP pinned layer structure includes at least two Fe-containing pinnedlayers having magnetic moments that are self-pinned antiparallel to eachother, the pinned layers being separated by an AP coupling layer of Cr.

In a preferred embodiment, the high coercivity structure includes alayer of CoPtCr or other high coercivity material. The CoPtCr ispreferably formed directly on one of the Fe-containing pinned layers ofthe AP pinned layer structure to avoid the necessity of any amorphousseed layer.

In one embodiment, the free layer includes a layer of Fe. The free layermay also be a multi-layer stack, e.g., further including a layer ofNiFe.

The structure preferably includes a spacer layer of Cr positionedbetween the free layer and the AP pinned layer structure. A head asrecited in claim 1, wherein the high coercivity layer is formed ofCoPtCr.

The head described herein may form part of a GMR head, a CPP GMR sensor,a CPP tunnel valve sensor, etc. for use in a magnetic storage system.

Other aspects and advantages of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the presentinvention, as well as the preferred mode of use, reference should bemade to the following detailed description read in conjunction with theaccompanying drawings.

FIG. 1A is an air bearing surface view, not to scale, of a prior artspin valve (SV) sensor.

FIG. 1B is an air bearing surface view, not to scale, of a prior artkeepered SV sensor.

FIG. 2 is an air bearing surface view, not to scale, of a prior artAP-Pinned SV sensor.

FIG. 3 is a simplified drawing of a magnetic recording disk drivesystem.

FIG. 4 is a partial view of the slider and a merged magnetic head.

FIG. 5 is a partial ABS view, not to scale, of the slider taken alongplane 5—5 of FIG. 4 to show the read and write elements of the mergedmagnetic head.

FIG. 6 is an enlarged isometric illustration, not to scale, of the readhead with a spin valve sensor.

FIG. 7 is an ABS illustration of a CPP GMR sensor, not to scale,according to an embodiment of the present invention.

FIG. 8 is an ABS illustration of a CPP tunnel valve sensor, not toscale, according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following description is the best embodiment presently contemplatedfor carrying out the present invention. This description is made for thepurpose of illustrating the general principles of the present inventionand is not meant to limit the inventive concepts claimed herein.

Referring now to FIG. 3, there is shown a disk drive 300 embodying thepresent invention. As shown in FIG. 3, at least one rotatable magneticdisk 312 is supported on a spindle 314 and rotated by a disk drive motor318. The magnetic recording on each disk is in the form of an annularpattern of concentric data tracks (not shown) on the disk 312.

At least one slider 313 is positioned near the disk 312, each slider 313supporting one or more magnetic read/write heads 321. More informationregarding such heads 321 will be set forth hereinafter during referenceto FIG. 4. As the disks rotate, slider 313 is moved radially in and outover disk surface 322 so that heads 321 may access different tracks ofthe disk where desired data are recorded. Each slider 313 is attached toan actuator arm 319 by means way of a suspension 315. The suspension 315provides a slight spring force which biases slider 313 against the disksurface 322. Each actuator arm 319 is attached to an actuator means 327.The actuator means 327 as shown in FIG. 3 may be a voice coil motor(VCM). The VCM comprises a coil movable within a fixed magnetic field,the direction and speed of the coil movements being controlled by themotor current signals supplied by controller 329.

During operation of the disk storage system, the rotation of disk 312generates an air bearing between slider 313 and disk surface 322 whichexerts an upward force or lift on the slider. The air bearing thuscounter-balances the slight spring force of suspension 315 and supportsslider 313 off and slightly above the disk surface by a small,substantially constant spacing during normal operation.

The various components of the disk storage system are controlled inoperation by control signals generated by control unit 329, such asaccess control signals and internal clock signals. Typically, controlunit 329 comprises logic control circuits, storage means and amicroprocessor. The control unit 329 generates control signals tocontrol various system operations such as drive motor control signals online 323 and head position and seek control signals on line 328. Thecontrol signals on line 328 provide the desired current profiles tooptimally move and position slider 313 to the desired data track on disk312. Read and write signals are communicated to and from read/writeheads 321 by way of recording channel 325.

The above description of a typical magnetic disk storage system, and theaccompanying illustration of FIG. 3 are for representation purposesonly. It should be apparent that disk storage systems may contain alarge number of disks and actuators, and each actuator may support anumber of sliders.

FIG. 4 is a side cross-sectional elevation view of a merged magnetichead 400, which includes a write head portion 402 and a read headportion 404, the read head portion employing a dual spin valve sensor406 of the present invention. FIG. 5 is an ABS view of FIG. 4. The spinvalve sensor 406 is sandwiched between nonmagnetic electricallyinsulative first and second read gap layers 408 and 410, and the readgap layers are sandwiched between ferromagnetic first and second shieldlayers 412 and 414. In response to external magnetic fields, theresistance of the spin valve sensor 406 changes. A sense current (I_(s))conducted through the sensor causes these resistance changes to bemanifested as potential changes. These potential changes are thenprocessed as readback signals by the processing circuitry 329 shown inFIG. 3.

The write head portion 402 of the magnetic head 400 includes a coillayer 422 sandwiched between first and second insulation layers 416 and418. A third insulation layer 420 may be employed for planarizing thehead to eliminate ripples in the second insulation layer caused by thecoil layer 422. The first, second and third insulation layers arereferred to in the art as an “insulation stack”. The coil layer 422 andthe first, second and third insulation layers 416, 418 and 420 aresandwiched between first and second pole piece layers 424 and 426. Thefirst and second pole piece layers 424 and 426 are magnetically coupledat a back gap 428 and have first and second pole tips 430 and 432 whichare separated by a write gap layer 434 at the ABS. Since the secondshield layer 414 and the first pole piece layer 424 are a common layerthis head is known as a merged head. In a piggyback head an insulationlayer is located between a second shield layer and a first pole piecelayer. First and second solder connections (not shown) connect leads(not shown) from the spin valve sensor 406 to leads (not shown) on theslider 313 (FIG. 3), and third and fourth solder connections (not shown)connect leads (not shown) from the coil 422 to leads (not shown) on thesuspension.

FIG. 6 is an enlarged isometric ABS illustration of the read head 400shown in FIG. 4. The read head 400 includes the spin valve sensor 406.First and second hard bias and lead layers 602 and 604 are connected tofirst and second side edges 606 and 608 of the spin valve sensor. Thisconnection is known in the art as a contiguous junction and is fullydescribed in U.S. Pat. No. 5,018,037 which is incorporated by referenceherein. The first hard bias and lead layers 602 include a first hardbias layer 610 and a first lead layer 612 and the second hard bias andlead layers 604 include a second hard bias layer 614 and a second leadlayer 616. The hard bias layers 610 and 614 cause magnetic fields toextend longitudinally through the spin valve sensor 406 for stabilizingthe magnetic domains therein. The spin valve sensor 406 and the firstand second hard bias and lead layers 602 and 604 are located between thenonmagnetic electrically insulative first and second read gap layers 408and 410. The first and second read gap layers 408 and 410 are, in turn,located between the ferromagnetic first and second shield layers 412 and414.

The present invention provides a new sensor structure having a thinnerpinned structure together with reduced current shunting to optimizedr/R. Many types of heads can use the structure described herein, andthe structure is particularly adapted to a CPP GMR sensor and a CPPtunnel valve sensor. In the following description, the width of thelayers (W) refers to the track width. The sensor height is in adirection into the face of the paper. Unless otherwise described,thicknesses of the individual layers are taken perpendicular to theplane of the associated layer, and are provided by way of example onlyand may be larger and/or smaller than those listed. Similarly, thematerials listed herein are provided by way of example only, and oneskilled in the art will understand that other materials may be usedwithout straying from the spirit and scope of the present invention.

CPP GMR

FIG. 7 depicts an ABS view of a CPP GMR sensor 700 according to oneembodiment. “CPP” means that the sensing current (I_(s)) flows from oneshield to the other shield in a direction perpendicular to the plane ofthe layers forming the sensor 700.

As shown in FIG. 7, a first shield layer (S1) 702 is formed on asubstrate (not shown). The first shield layer 702 can be of any suitablematerial, such as permalloy (NiFe).

Seed layers are formed on the first shield layer 702. The seed layersaid in creating the proper growth structure of the layers above them.Illustrative materials formed in a stack from the first shield layer 702are a layer of Ta (SL1) 704 and a layer of NiFeCr (SL2) 706.Illustrative thicknesses of these materials are Ta (30 Å), NiFeCr (20Å). Note that the stack of seed layers can be varied, and layers may beadded or omitted based on the desired processing parameters.

A free layer (FL) 710 is formed above the seed layers 704–708. Themagnetic moment of the free layer 710 is soft and so is susceptible toreorientation from external magnetic forces, such as those exerted bydata on disk media. The relative motion of magnetic orientation of thefree layer 710 when affected by data bits on disk media createsvariations in the sensing current flowing through the sensor 700,thereby creating the signal. Preferred materials for the free layer 710are a NiFe/Fe stack (FL1, FL2) 712, 714, but can also be formed of aCoFe/Fe stack, a CoFe/NiFe/Fe stack, etc. An illustrative thickness ofthe free layer 710 is about 10–40 Å.

The magnetic orientation of the free layer 710 must be preset duringmanufacture, otherwise the orientation will be unstable and could movearound at random, resulting in a “scrambled” or noisy signal. Thisinstability is a fundamental property of soft materials, making themsusceptible to any external magnetic perturbations. Thus, the magneticorientation of the free layer 710 should be stabilized so that when itsmagnetic orientation moves, it consistently moves around in asystematical manner rather than a random manner. The magneticorientation of the free layer 710 should also be stabilized so that itis less susceptible to reorientation, i.e., reversing. Usually hardmagnet layers (not shown) are placed adjacent to the edges of the freelayer 710 to stabilize the free layer.

A spacer layer (SP) 716 is formed above the free layer 710. The spacerlayer 716 is preferably formed of Cr. An exemplary thickness of thespacer layer 716 is about 10–30 Å, more preferably about 15–25 Å, andideally about 20 Å.

Then an antiparallel (AP) pinned layer structure 722 is formed above thespacer layer 716. As shown in FIG. 7, first and second AP pinnedmagnetic layers, (AP1) and (AP2) 724, 726, are separated by a thin layerof an antiparallel coupling (APC) material 728 such that the magneticmoments of the AP pinned layers 724, 726 are self-pinned antiparallel toeach other. The pinned layers 724, 726 have a property known asmagnetostriction. The magnetostriction of the pinned layers 724, 726 isvery positive. The sensor 700 is also under compressive stresses becauseof its geometry at the ABS, and the configuration of the layer is suchthat it produces very large compressive stress. The combination ofpositive magnetostriction and compressive stress causes the pinnedlayers 724, 726 to develop a magnetic anisotropy that is in aperpendicular direction to the track width. This magnetic couplingthrough the AP coupling material 728 causes the pinned layers 724, 726to have antiparallel-oriented magnetizations.

In the embodiment shown in FIG. 7, the preferred magnetic orientation ofthe pinned layers 724, 726 is for the first pinned layer 724, into theface of the structure depicted (perpendicular to the ABS of the sensor700), and out of the face for the second pinned layer 726. The pinnedlayers 724, 726 are formed of an Fe-containing material, preferablysubstantially pure Fe, separated by an antiparallel coupling layer 728of Cr. Illustrative thicknesses of the first and second pinned layers724, 726 are between about 10 Å and 25 Å. The Cr layer 728 can be about5–15 Å, but is preferably selected to provide a saturation field aboveabout 10 KOe. In a preferred embodiment, each of the pinned layers 724,726 is about 18 Å with a Cr layer 728 therebetween of about 8 Å.

In typical heads, the AP pinned layer structure 722 is stabilized byplacement of an antiferromagnetic (AFM) layer above the pinned layerstructure 722. The AFM layer pins the AP pinned layer structure 722 sothat the pinned layers 724, 726 do not move around when disk is readingdata from disk, upon application of external magnetic fields, etc.However, as mentioned above, AFM layers are very thick, typically about150–200 Å. If the designer wants to fit the sensor into small gap, useof thick AFM layers is not practical.

To reduce the overall thickness of the sensor 700 while providing thedesired stabilizing effect, a high coercivity layer 730 is formed abovethe pinned layer structure 722. The high coercivity layer 730 pins themagnetic orientation of the second pinned layer 726, stabilizing theoverall pinned layer structure 722.

The preferred material for the high coercivity layer 730 is CoPtCr,though other hard magnet materials can also be used. CoPtCr has acoercivity of greater than about 1000 Oe, and is sometimes used in harddisk media. This high coercivity pins the second pinned layer 726. Apreferred thickness of the high coercivity layer 730 is about 10–50 Å,ideally about 30 Å.

CoPtCr has a crystalline structure. Because the CoPtCr layer 730 isformed on the second pinned layer 726 of Fe, no seed layer is necessaryto obtain proper physical growth of CoPtCr structure. This furtherreduces the thickness of the overall sensor 700.

A cap (CAP) 738 is formed above the high coercivity layer 736. Exemplarymaterials for the cap 738 are Ta, Ta/Ru stack, etc. An illustrativethickness of the cap 738 is 20–40 Å.

A second shield layer (S2) 740 is formed above the cap 738. Aninsulative material 742 such as Al₂O₃ is formed on both sides of thesensor 700.

The inventor has found that the structure disclosed herein providesabout ten times the magnetoresistance of a Co/Cr/Co CPP structure.

Note that in some embodiments, the first pinned layer 724 (e.g., of Fe)generates magnetoresistance with the Cr spacer layer 716. Becausemagentoresistance is a function of magnetic thickness, and because thesecond pinned layer 726 (e.g., of Fe) and the high coercivity layer 730above it are magnetic, it is desirable to obtain a total magneticthickness of the second pinned layer 726 and the high coercivity layer730 comparable to that of the first pinned layer 724. Thus, the secondpinned layer 726 is preferably thinner than the first pinned layer 724to reduce canceling of the magnetoresistive signal by the second pinnedlayer 726. This results in a larger net magnetoresistive signal.

One practicing the invention can determine the appropriate magneticthickness of the layers using the following equation:Magnetic thickness=M×T  Equation 1where:

-   -   M=magnetization=magnetic moment per unit volume (emu/cm³);    -   T=physical thickness (cm); and    -   emu=electromagnetic unit.

CPP Tunnel Valve

FIG. 8 depicts an ABS view of a CPP tunnel valve sensor 800 according toone embodiment. The CPP tunnel valve sensor 800 generally has the sameconfiguration as the structure shown in FIG. 7, except that the spacerlayer 716 is formed of a dielectric barrier material, such as, Al₂O₃,AlO_(x), MgO_(x), etc. The spacer layer 716 is very thin such that theelectric current passing through the sensor 800 “tunnels” through thespacer layer 716. An illustrative thickness of the spacer layer 716 is3–6 Å.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. For example, the structures and methodologies presentedherein are generic in their application to all MR heads, AMR heads, GMRheads, spin valve heads, etc. Thus, the breadth and scope of a preferredembodiment should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A magnetic head, comprising: a free layer; an antiparrallel (AP) pinned layer structure spaced apart from the free layer, the AP pinned layer structure includes at least two substantially pure Fe pinned layers having magnetic moments that are self-pinned antiparallel to each other, the pinned layers being separated by an AP coupling layer of Cr; and a high coercivity layer positioned towards the AP pinned layer structure on an opposite side thereof relative to the free layer, the high coercivity structure pinning a magnetic orientation of the AP pinned layer structure.
 2. A head as recited in claim 1, wherein the free layer includes a layer of substantially pure Fe.
 3. A head as recited in claim 2, wherein the free layer further includes a layer of NiFe.
 4. A head as recited in claim 1, further comprising, a spacer layer of Cr positioned between the free layer and the AP pinned layer structure.
 5. A head as recited in claim 4, wherein the spacer layer has a thickness of between about 15 and 25 Å.
 6. A head as recited in claim 1, wherein the head forms part of a GMR head.
 7. A head as recited in claim 1, wherein the head forms part of a CPP GMR sensor.
 8. A head as recited in claim 1, wherein the head forms part of a tunnel valve sensor.
 9. A magnetic storage system comprising: magnetic media; at least one head for reading from and writing to the magnetic media, each head having: a sensor having the structure recited in claim 1, a writer coupled to the sensor; a slider for supporting the head; and a control unit coupled to the head for controlling operation of the head.
 10. A magnetic head comprising: a free layer; an antiparallel (AP) pinned layer structure spaced apart from the free layer, the AP pinned layer structure includes at least two Fe-containing pinned layers having magnetic moments that are self-pinned antiparallel to each other, the pinned layers being separated by an AP coupling layer of Cr; and a high coecivity layer positioned towards the AP pinned layer structure on an opposite side thereof relative to the free layer, the high coercivity structure pinning a magnetic orientation of the AP pinned layer structure, wherein the high coercivity layer is formed of CoPtCr.
 11. A head as recited in claim 10, wherein the CoPtCr is formed directly on one of the Fe-containing pinned layers of the AP pinned layer structure.
 12. A magnetic head, comprising: a free layer, the free layer including a layer of Fe; an antiparallel (AP) pinned layer structure spaced apart from the free layer, the AP pinned layer structure includes at least two Fe-containing pinned layers having magnetic moments that are self-pinned antiparallel to each other, the pinned layers being separated by an AP coupling layer of Cr, wherein one of the pinned layers is thicker than another of the pinned layers; a spacer layer of Cr positioned between the free layer and AP pinned layer structure; and a high coercivity layer positioned towards the AP pinned layer structure on an opposite side thereof relative to the free layer, the high coercivity structure pinning a magnetic orientation of the AP pinned layer structure.
 13. A lead as recited in claim 12, wherein the free layer further includes a layer of NiFe.
 14. A head as recited in claim 12, wherein the layer of Fe in the free layer is substantially pure Fe.
 15. A head as recited in claim 12, wherein the spacer layer has a thickness of between about 15 and 25 Å.
 16. A head as recited in claim 12, wherein the head forms part of a GMR head.
 17. A head as recited in claim 12, wherein the head forms part of a CPP GMR sensor or a tunnel valve sensor.
 18. A head as recited in claim 12, wherein a total magnetic thickness of one of the pinned layers and the high coercivity layer combined is about the same as a magnetic thickness of another of the pinned layers.
 19. A magnetic storage system, comprising: magnetic media; at least one head for reading from and writing to the magnetic media, each head having: a sensor having the structure recited in claim 12; a writer coupled to the sensor; a slider for supporting the head; and a control unit coupled to the head for controlling operation of the head.
 20. A magnetic head comprising: a free layer, the free layer including a layer of Fe; an antiparallel (AP) pinned layer structure spaced apart from the free layer, the AP pinned layer structure includes at least two Fe-containing pinned layers having magnetic moments that are self-pinned antiparallel to each other, the pinned layers being separated by an AP coupling layer of Cr; a spacer layer of Cr positioned between the free layer and AP pinned layer structure; and a high coercivity layer positioned towards the AP pinned layer structure on an opposite side thereof relative to the free layer, the high coercivity structure pinning a magnetic orientation of the AP pinned layer structure, wherein the high coercivity layer is formed of CoPtCr.
 21. A head as recited in claim 20, wherein the CoPtCr is formed directly on one of the Fe-containing pinned layers of the AP pinned layer structure. 